Laser induced surface modification has been used to fabricate conducting paths in ceramic substrates. For the purpose of process simulation and prediction of process parameters a finite element model has been developed to simulate the thermal behaviour of the substrate during laser surface interaction. The results of the model calculation have been completely verified experimentally for alumina substrates. Using this model the width and the depth of the fabricated lines could be predicted as a function of the laser power and velocity. First results are presented for Cordierite substrates. Further developments will consider different ceramic substrates such as PZT.